Phineas and Ferb: Welcome to the First Dimension
by humilityhehe
Summary: One dimension? An opportunity. Two dimensions? An adventure. Three dimensions? That's just too much. Join Phineas, Ferb, and their friends as they save the world once again but this time from an enemy they never expected. T - for evil
1. Prologue

Prologue: Summer

"Ferb, I know what we're going to do today."

It's been six years since that one summer day when the famous brother, Phineas and Ferb visited the second dimension. They might have forgotten all of the things they did on that day but it didn't mean time would stop just like that because today would be the day when the fate of multiple world come together again.

"We're going to build a dimensional transporter," the red haired boy finished. It was the start of summer with school just started and the two brothers-of-invention were once again making the impossible possible back in their backyard. Phineas wore an orange hoody with blue jeans while Ferb sported a white long-sleeve polo with a vest on top, wearing black slacks.

Ferb gave his brother a thumbs-up and took out a blueprint from his pocket. He started unfolding the small piece of paper until it was twice their sizes.

"Where did you get that Ferb?" the green haired boy simply shrugged. "Well never mind that, we better get started before the day ends."

The two smiled and started taking out the things they would need from their room. There were screwdrivers, nails, a hammer, a few nuts and bolts, and a few other things a pair of teenagers would never be seen using anywhere else except for Danville.

The entire backyard was filled with the sound of welding and a hammer repeatedly hitting a nail. The boys sure worked fast since it didn't even took half a day and their little project was already taking shape. But let's take a break from our friends' little experiment and see the events unfolding on another dimension.

The second dimension, a world that used to be under the control of the evil- and I mean _the_ evil Heinz Doofenshmirtz. Compared to the state it was back then, you would have expected something good to happen. But sadly that's just not how things were looking. Burn marks could be seen on everything. There were holes on the houses and cracks on the streets. The entire place looked better when it was still under Doofenshmirtz control. But what of the Phineas and Ferb of this dimension, what were they doing?

"Are you ready Ferb," the voice over the communicator asked. It was Candice Flynn, Phineas and Ferb's older sister. "Now remember the plan and don't get caught."

"Roger," Ferb replied, turning off his communicator. Ferb was wearing a black fatigue, a green bandana, and a pair of shades. He took a deep breath and held his gun closer. His thoughts wondered off as he waited for the signal, remembering the fun he had with his brother and their friends back when they defeated Doofenshmirtz.

But all of the pleasant memories of spending summer, doing things ordinary teenagers would do didn't last. Four years after their liberation a new threat came and took aware their hard earned freedom once again.

A huge explosion brought back Ferb from his walk down memory lane. It was the signal he has been waiting for. He quickly stood up and ran for the tower's entrance, ignoring the battle between the evil robots and the fireside girls. Once inside, he quietly made his way through the corridor and into the upper floors. But t wasn't easy. Left over guards patrolled through the winding corridors and traps were scattered through out the complex, all armed and dangerous. But Ferb was trained for this; he spent most of the two years fighting against the growing menace and was a master in espionage.

Finally at the top, there was only a single door left separating him from his destination. He walked up the door and turned the knob, slowly pushing the door open. Once inside, a small pink room was all to greet him. It had a queen-size bed on one corner and a small desk on the other. It looked more like a girl's room rather than that of a world conqueror.

"It seems like you've finally come, Ferb," A familiar voice echoed through the room. But Ferb simply stood there, listening to the person's voice. "I see you're still mad with what happened to your brother, Phi-"

"-Don't you dare say utter his name," Ferb interrupted.

A loud metallic sound came from behind the green haired soldier, where a throne made from gold and pink slowly rose.

"It seems like you've become a man of words since the last time we saw each other," the figure sitting on the throne taunted.

"And you didn't change at all," Ferb replied. "You're still the evil witch that stole everything from us."

"How harsh. I simply took everything that belonged to me, is that so bad?"

"None of these are yours." Ferb took his rifle and aimed it at the figure. "Now quietly step down from there and follow me. Your reign of tyranny ends here, Isabella."

Isabella grinned and stood up, slowly walking down from her throne.


	2. One Isabella, Two Isa Wait, What?

Chapter 1: One Isabella, two Isa… wait, What?

It was already 12 in the afternoon when the brothers of invention finished the day's project. In place of all the junk that used to be scattered through the backyard that morning, there was now a machine twice their height. It had a ray gun mounted on the very top and a circular base.

"We did it Ferb," the red haired boy stated. "With this we can finally move through dimensions."

"If the matter accelerator doesn't scramble our particles first," Ferb said.

"Don't be a killjoy Ferb," Phineas frowned and beamed a smile again. "Nothing ever goes wrong with our projects. I mean besides mysteriously disappearing that is. And talking about mysterious disappearances, where's Perry?"

Talking about Perry, our favorite semi-aquatic mammal was once again sneaking away from his boys. Sliding down the pipe hidden behind a secret door found on a wall, he landed safely on his seat inside his secret base. Greeting Sgt. Monogram on the screen.

"Good Day, Agent P," Sgt. Monogram greeted. "Dr. Doofenshmirtz won't be our priority today. He seems to be busy with something back in his hometown so he won't be bothering us for a little while." Perry breath a sigh of relief as he wiped imaginary swear off his furry head. "But there seems to be a suspicious group in downtown Danville doing something we are yet to identify. It's your job to find out what they're up to and if it's evil, stop it." Perry nodded. "Good luck Agent P." With those parting words Perry pressed a button, sending him through a hole on the ceiling and into the sky where a jet plane was waiting for him.

Perry pressed the ignition button and was immediately on his way to downtown. The scene changed from that of a cheerful metropolis into that of a gloomy slum. The houses were all aging with the windows bare, fire lit on trashcans, and homeless people littered through the dark corners of the streets. If you were oblivious to this part of Danville, then you'll definitely think you're in a completely different place.

After a few minutes of flying around downtown, Perry noticed a few well-dressed men walking in and out of an abandoned building. Landing on the opposite building, Perry took out his binoculars and started observing the suspicious individuals.

Perry noticed three things. First, there were only two of them. They would come in and out of the building, taking a box from the truck parked up front with them every time they came out. Second, It was hard to identify the content of the boxes. There weren't any label or print on the boxes to identify what they had inside and it didn't look like the men had any open ones in the truck. And lastly, they were clearly up to no-good. No one in their clear mind would think these people were in downtown to set up a business, and to have three really well dressed macho men coming in and out of an abandoned building? That just spells trouble, and Agent P. wasn't going to let that happen.

Waiting for both to walk inside, Perry took off his hat and jumped off the roof once the coast was clear. Walking towards the door like he was a normal platypus, one of the thugs came out.

"What the," he shouted, stopping right in front of the door. "Hey! hey, Look!"

"What is it Marco," the older looking one asked, walking right behind Marco.

"Look Jeff, it's a Platypus," Marco stated the obvious, pointing at our hero.

"I can see that," Jeff sighed.

"Aren't you a little bit surprised to see one in the middle of the city? Downtown even. Maybe it's one of those animal spies we keep hearing about."

"That's impossible numbskull." Jeff slapped the back of Marco's head then went and pointed at our friend. "It's a platypus, they don't do much." Perry chattered. "And it might have just escaped from a pet store or something. Anyway, just get back to work. The boss called and he said he's right on his way. So we better hurry this up before we get killed."

"Okay," Marco replied, picking up another box. He walked up the door before stopping in front of Perry. "You better ran away now little guy. You don't want to stay here when the boss come, he's really evil."

"MARCO!"

"Anyway, I better go," Marco said and ran into the building.

Perry chattered once more, baffled by the way the two acted. But it didn't take long before he regained his composure and walked into the building, melding into the shadows and passing through the corridors of the abandoned place. But we're getting ahead of ourselves, so why don't we turn back a few minutes and look at the things unfolding in the Flynn-Fletcher backyard.

While Perry was getting brief in his base, Isabella came over and was already chatting it off with the brothers. She was wearing a violet t-shirt with blue jeans that cuts of below her knee. She also had her hair tied into a ponytail.

"Hi Phineas," Isabella greeted her crush. You would have thought Phineas has already realized the poor girl's feelings for him but it seems like time hasn't changed that much since the boy genius was still as oblivious as ever. "Whatcha doing?"

"Oh Isabella." Phineas greeted her back with a smile. "You just came in time to see us test our dimensional transporter."

"Dimensional transporter," Isabella asked. "Isn't that a little bit too dangerous?"

"What's with you and Ferb today," Phineas frowned. "When did our experiment ever go wrong?"

"It's not like that Phineas," Isabella reassured the boy. "Something just doesn't feel right about that thing." The green haired boy simply nodded to this.

"Well I say let's test it our first," Phineas suggested. "Nothing bad about testing it our right? If it doesn't work then we'll disassemble it and maybe build something else in the afternoon."

Ferb and Isabella could only nod at this, but what Isabella said was true. Both couldn't explain it but something about that machine just feels wrong. Ferb felt it the moment they finished it and Isabella felt it the first time she heard its name. Both knew something would definitely go wrong.

Phineas walked towards the control panel behind the machine and asked the two to step under the ray gun. After pressing a few buttons, Phineas ran under onto the base as well while the ray gun took its time charging on top of them. Phineas' eyes beamed with excitement while his two companions only felt more and more anxious as the ray gun charged.

The machine has reached the required energy output and was now preparing to fire. Phineas was as prepared as he could be. He closed his eyes waiting for the ray to hit them and send them flying through the dimensions. But the awaited zap never came. Each passing second only further lowered the boy's enthusiasm. Opening his eyes, Phineas was a little disappointed as he looked at the ray gun above him and all it did was emit smoke.

"That's weird." Phineas scratched the back of his head. "I swore all the calculations we're correct." Phineas finished, walking off the device along with his friends. But once of, the most unexpected thing happened, a large beam shot out from the gun and hits the base of the device, creating a lot of smoke.

"Phineas," Isabella shouted, coughing from behind the thick layer of smoke.

"I'm right hear Isabella," Phineas replied. "Is everyone alright?"

Some of the smoke cleared, allowing the three to get their bearing. None of them looked hurt and except for the large quantity of smoke floating over the device nothing seemed to have been damage. Phineas looked around after asking his question and after getting two nods turned his attention back at the machine.

The smoke was slowly clearing around the transporter and there was not a scratch on it. All of the parts were there but there _was_ one small detail that wasn't there before the explosion. A girl around the same age as Isabella, wait scratch that. Looking at her a lot closer. It _was_ Isabella, another Isabella in fact.

"Whe- where am I," the disoriented second Isabella asked, coughing a few times. But none of the three gave her a reply. How could they? They were all too shocked to even move. This wasn't supposed to happen. Phineas and Ferb looked shock because it's the first time anything like this happened with one of their inventions. Isabella on the other hand looked shock because she was staring at herself. Another _her_ that supposedly came from another dimension. It seems like things aren't playing out for the Phineas and Ferb of this dimension, so what about the ones of the second dimension?

The rebel headquarters were in an uproar. The alarms were set off and the fireside girls were running all over the place. Let's visit the strategy room. Maybe we'll get some answer from there.

"What do you mean she escaped," Candace shouted at one of the fireside girls, slamming his hands onto the table.

"There was a huge hole in her cell when we checked ma'am," Ginger saluted, flinching when the older Flynn slammed the table.

"We placed her in maximum security and she was still able to escape. Get everyone available into the search and don't let any nook or cranny unchecked. That woman can't be allowed to escape."

The trebling girl gave her officer a salute and dashed out of the room, leaving the raging woman with his stepbrother. Ferb simply stared at the space the fireside girl stood. He couldn't believe what he just heard. The world's most dangerous criminal was out there once again ready to plan their demise.

**Hi guys, thank you for those who has subscribed and will subscribed to this story. It's been a while since I wrote something new so, the writings a little… hehehe… Anyway, until next time. **


	3. Similarities

Chapter 2: Similar

"Whe- where am I," the disoriented teenager from another dimension asked. But no one responded. Phineas, Ferb, and the Isabella of that dimension simply stood there. They didn't know what to do. First, Phineas' invention malfunction then another Isabella gets transported from her dimension into theirs. What could happen next?

"Phineas," the other Isabella asked, getting a clearer picture of her surrounding after the smoke started clearing. "Phineas is that you?"

"Not the one you might know," Phineas replied halfheartedly.

"Wai- wait," the other Isabella ignored the boy's reply, shifting her gaze from him to the girl beside him. "Is… is that me? What's happening?"

"Calm down… Isabella." Phineas walked up to the girl and gave her a supporting hand on the shoulder before she completely broke down. But to his surprise, the girl started crying on his chest, the Isabella of that world didn't like one bit though. "Phineas," she said between sobs. "Where, where are we?"

"Uhm… You're in another dimension Isabella," the red haired boy explained. "And I'm not exactly the Phineas you might know."

Hearing this, the girl parted from the boy's chest and gave him an analytical look, taking in everything about the boy. He on the other hand got to see the girl up close, there wasn't much different from their Isabella except for the clothes and maybe who knows, her personality. She wore a white, short-sleeve polo with a matching pink skirt. But he was snapped out of it when the girl pushed herself away.

"Where am I," she asked again. It looked like she still hasn't got over the initial shock. "And what do you mean 'another dimension'?"

"Well, it started out like this," Phineas explained everything to her and how their experiment failed and how they brought her over there by mistake. "I'm really sorry."

"Wait," she stopped him before he could apologize again. "You guys invented this thing? Aren't you guys a little too young to mess with the fabric of time and space?"

Phineas and Ferb exchanged looks and then the former replied, "Yes, yes we are." The second Isabella gave off a small giggle, confirming that she has already gotten over the initial shock.

"But what do you guys plan to do now? I can't stay here forever right?"

"Well, we are planning on sending you back immediately but…" Phineas looked at the device and noticed some smoke coming out of the control panel and the gun. "I doubt it would be safe without repairing it first."

"That means I'm stuck here for now, right," the other Isabella asked. The red haired boy nodded. "Then it's settled then." She stood up and dusted her skirt and walked away from the base. "Please do take care of me."

"Then allow me to introduce ourselves," Phineas said, following the girl out of the base. "I'm Phineas Flynn, that's my brother Ferb Fletcher, and that's this world's Isabella Garcia-Shapiro."

"It's nice to meet you guys, you can call me Isa seeing it'll be a huge problem having to call two Isabellas that look exactly the same." Isa gave her counterpart a smile, and Isabella returned it with a smile of her own. "But there is one problem though, where will I stay."

"That is a problem," Phineas agreed.

"I don't mind," Isabella said, offering her place to her counterpart. Her actual reason though was to avoid having the girl stay over at Phineas' place. "It would be like having a twin sister and I doubt my mom would mind."

"Then that settles it," Phineas beamed, returning to his old self. "Welcome aboard Isa!"

It seems like things are looking better here at the Flynn-Fletcher residence after the brothers' major screw up. But what about Perry, is he getting anywhere with his mission? Getting back to our semi-aquatic spy, it seems like he has already gotten quite deep into the building, where the thugs were dropping off some suspicious boxes.

Perry was hiding behind one of the boxes, when Marco dropped off the last one. They were in one of the unused room on the third floor and it already looked nothing like the rest of the rooms on the building. There were thousands of boxes scattered though out the room, pile after pile of boxes stacked on top of each other.

"That's the last one," Marco said, wiping off the sweat forming on his forehead.

"Good," Jeff said, taking a look at his watch. "And we're just in time. The boss should already be here. All we have to do now is wait for his orders and we're done with phase one."

"I'm really excited about this, Jeff."

"Yeah," Jeff nodded. "But whoever hired us is really evil. Taking over the entire world is no small feet you know."

Perry's eyes widen as he took in this bit of information. It looks like who ever he was up against this time was truly planning something outrageous. He was about to charge into the scene when Jeff said something else that caught his interest.

"Now to open these babies up. Hey Marco, toss me that lever over." Marco did as he was told. Pushing in the lever between the lid and body of the first box, Jeff pushed all of his strength into opening it. A small pop came from the lid and it came flying off. Perry couldn't believe what he saw, there were small packages of powered juice inside the box. "With these babies taking over the world won't be that hard."

Perry did the best thing he could think of at that time, he slammed his head on the boxes he was hiding behind and shook his head. The supposedly suspicious people were actually part of juice industry. But how he could be so sure they weren't some sorts of mind controlling powder? Well Marco and Jeff actually drunk some to further erase any doubt. If only Perry could swear, he would swear that all the suspicious people that come into Danville were all pretty much harmless. But he couldn't so he does the next best thing, he chattered away like any annoyed Platypus would do.

But that's enough with Perry it doesn't look like he'll be coming across any danger this time. But what about the situation in the second dimension, is the situation over there getting any better?

Well, Candace could be seen walking back and forth in her office when Ferb came in. Candace gave him a stern look but loosened up. She knew the boy was also having a hard, especially after finding out the person who took their brother away from them was now running lose out there and with our any clues to tract her with.

"So any update from the girls?"

"None so far. Everywhere they looked would lead them to a dead end. It's as if Isabella just disappeared into thin air."

"Are you sure? How about Baljeet?"

"None from his as well, he keeps telling me that her signature is just not showing up. I'm afraid that that witch has created another contraption to escape our grasp once again."

"If only Phineas was here," Candace sighed. "Call back all the girls and regroup, she's definitely out there, and we'll just have to search every nook and cranny if we have to just to smoke her out. But for now take a rest. We all need it."

Ferb gave her stepsister a salute and walked out of the room. He was nowhere finished yet, but Candace was right- she was always right. He needed a break and maybe who knows maybe it'll help clear up his mind. A lot of things happened that day but he knew the things that would happen the next few days would be like nothing they have experienced before.

**And here's the third chapter, please do give me a review about my writing and it'll definitely encourage me to write more and maybe improve the quality of this fic. **


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